We are studying T cell antigen receptors (TCR) with the purpose of more fully understanding the requirements for their activation in an immune response. The two broad classes of TCR, alpha/beta TCR and gamma/delta TCR, are both under investigation. The co-receptors CD8 and CD3 are also being studied. Our goal is to analyze these proteins biochemically and structurally. To do so requires that we produce sufficient amounts of protein for study and that we characterize the recombinant proteins for their appropriate functionality. Further study of their binding to ligands and of their three-dimensional structure by X-ray crystallography should lead to insights as to how these proteins function in the immune system. - T cell receptors, CD8, CD3, protein crystallography, biochemistry.